1. Field of the Invention
The present invention relates to a method and composition for reducing the production of sludge upon acid contact with sludging crude oil, and more particularly, to an improved sludge inhibiting acidizing composition and method of use.
2. Description of the Prior Art
The treatment of a hydrocarbon-containing subterranean formation with an aqueous acid solution is a commonly used technique for stimulating the production of hydrocarbons from the formation. Such a treatment generally includes the pumping of an aqueous acid solution into the formation to dissolve acid soluble materials and produce enlarged flow channels therein whereby the permeability of the formation is increased. The increased permeability allows a greater rate of hydrocarbons to flow through the formation and into the well bore penetrating the formation.
Certain crude oils contained in subterranean formations produce sludge upon contact with aqueous acid solutions during the carrying out of acidizing treatments. The sludge formed is an asphalt-like material which precipitates in the formations and often plugs or clogs the enlarged flow channels formed therein. The treated formations are very slow to clean up, if at all, and often the acidizing treatments produce a decrease in permeability and reduction in oil production instead of an increase therein.
Studies of sludging crude oils and their reactions with acids have shown that the precipitates formed are mainly asphaltenes, resins, paraffins and other high molecular weight hydrocarbons which, once formed, are very difficult to remove from subterranean formations. An explanation of why and how sludges are formed and some methods of sludge prevention are described in the article entitled "Formation, Affect and Prevention of Asphaltene Sludges During Stimulation Treatments" by E. W. Moore et al., Journal of Petroleum Technology, September, 1965, pages 1023-1028.
Methods for preventing or reducing sludge formation upon contact between sludging oils and aqueous acid solutions have been developed and used heretofore. Such methods include combining certain anti-sludging agents and other additives with the aqueous acid solution whereby the formation of sludge is inhibited when the resulting acid mixture contacts sludging crude oils. While such techniques and acid mixtures have achieved varying degrees of success, the anti-sludging agents and other additives included in the acid mixtures have often separated even though various dispersants have been included therein. When the resulting non-homogeneous acid mixtures have contacted sludging oils in subterranean formations, separated portions of the acid mixtures have still caused the precipitation of sludge in the formations.
By the present invention an improved acidizing method and long-term homogeneous acid composition are provided whereby the production of sludge is effectively reduced.